Presently, the power supply of an area (called voltage domain below) of a semiconductor circuit is switched off by a switch outside the semiconductor circuit or by individual large switches on the semiconductor circuit. A voltage domain is understood to mean an area of the semiconductor circuit which has the same power supply with a uniform value of the voltage. The semiconductor circuit can then include one or more voltage domains.
When the power supply of a voltage domain of a semiconductor circuit is switched on or off by the switch outside the semiconductor circuit, a supply potential for the semiconductor circuit is connected via the switch to a supply pin or supply terminal of the semiconductor circuit. This means that, depending on the switch position, the supply pin is either connected to the supply potential or not. Additionally, a supply voltage line of the voltage domain is connected to the supply pin. When a control signal to control the power supply of the voltage domain is generated within the semiconductor circuit, a control pin of the semiconductor circuit carries the control signal to the switch outside the semiconductor circuit. In this case, the control signal is not be generated within the voltage domain to be switched, since this is sometimes switched off. In this case, two pins of the semiconductor circuit per voltage domain are used, so that the number of voltage domains in the case of a design in which the switch is outside the semiconductor circuit is greatly restricted. A further disadvantage of this design is that a connecting line for the control signal is laid through the semiconductor circuit to the control pin, and a supply voltage line is laid from the supply pin through the semiconductor circuit to the appropriate voltage domain, which results in a long line relative to the semiconductor circuit for the case that the voltage domain is a long way away from the appropriate pins of the semiconductor circuit. As well as the area requirement, a long supply voltage line results in a voltage drop, on the supply voltage line, of a magnitude corresponding to the line length. Additionally, with this design there is a supply voltage network for each voltage domain, but no global, regular supply voltage network which extends over the whole semiconductor circuit.
When the power supply of a voltage domain of the semiconductor circuit is switched on or off by the switch within the semiconductor circuit, a switch which is large relative to other components on the semiconductor circuit is used, to ensure that the switch can drive the currents which it switches without a great voltage drop. Particularly in the case of semiconductor circuits which are created using standard cell design, such a switch is outside those areas of the semiconductor circuit which are constructed using standard cells. Therefore, not only does a supply voltage line which carries the supply potential to the switch have a non-negligible length, but so does a supply voltage line which carries the supply potential which is switched through the switch to the appropriate voltage domain. Because of the length, a large voltage drop on these supply voltage lines occurs.